Rhyner (U.S. Pat. No. 1,693,120), Kimura (U.S. Pat. No. 4,648,646) and Tamura et al (U.S. Pat. No. 4,796,591) each disclose the use of a rack and pinion to adjust the position of a car seat. Rhyner discloses an adjustment mechanism comprising a hand wheel mounted on a shaft on which pinions are provided. Racks are provided on opposed sides of the bottom of the seat. Upon turning the hand wheel, the pinions rotate causing the cat seat, to which the rack is mounted, to move forwardly or rearwardly. This design is disadvantageous for use with an office chair or the like as it uses two widely spaced apart racks to provide transverse stability to the seat.
Kimura and Timura et al each also disclose the use of spaced apart racks. In addition, these references disclose multiple support and linking members between the seat and the floor of the car. The mechanism discloses a plurality of parts which are complicated to manufacture and are not suitable for use with an office chair or the like.
Ambasz (Canadian Patent No. 1,076,944) discloses a chair which operates on the principle of independent forward and backward movement of the seat and tilting of the back such that a chair may automatically adopt a configuration that will provide excellent anatomical support to a person seated in the chair. To this end, Ambasz discloses a seat which has on its underside, adjacent to the centre and removed from the sides, a pair of elongated sleeves of uniform internal cross-section which extend lengthwise. The sleeves are in telescoping and sliding relation on the seat support such that the seat is slidable forwardly and rearwardly. The seat is spring-loaded toward the rearward most position. Accordingly, one disadvantage of this design is that it does not permit the operator to fix the seat in a pre-set position with respect to the chair back.
Matthews et al (U.S. Pat. No. 5,035,466) discloses an ergonomic chair wherein the seat support member is movable between a forward seated position and a rearward seated position. The mounting means for the seat includes a channel having a generally dovetail shaped configuration and a runner having a mating of dovetail shaped configuration that slidably engages the channel. As with Ambasz, the mounting means also includes means for biasing the seat support member toward the rearward position. Thus, the user may selectively apply force while seated in the chair to adjust and retain the position of the seat support member in a desired position between the rearward and forward position of the seat. Upon standing, the user removes the external force from the seat and the contraction force of the biasing means (i.e. A spring) will urge the runner back towards its original rearward seated position. Thus, one disadvantage of Matthews et al is that the chair will not maintain itself in a pre-selected position while the user stands.
Olsen et al (U.S. Pat. No. 5,542,743) discloses a chair in which the seat member is movable with respect to the back-rest of the chair. The adjustment mechanism comprises a pair of parallel spaced tubular members telescopically received in the control bracket. The seat may be fixed in position by a clamping bar which clamps the tubular members to the control bracket. Accordingly, one disadvantage of this design is that, when the clamp is removed, there is no restriction on the movement of this seat with respect to the chair back. Accordingly, the seat would become free floating.
Accordingly, previous disclosures have shown seat adjustment mechanisms for chairs which do not provide adequate controlled adjustment of the position of the seat with respect of the seat support. In addition, prior designs have incorporated constructions which are difficult to employ and/or which are complicated to construct.